Emission treatment system and method of operation

ABSTRACT

An emission treatment system is provided. The emission treatment system comprises a separation system and a selective catalytic reduction (SCR) catalyst. The separation system comprises a separator, a fuel inlet disposed to supply fuel to the separator, a first fuel outlet and a second fuel outlet respectively disposed to carry away fuel from the separator. The SCR catalyst comprises a catalyst composition comprising silver and templated metal oxide substrate. The emission treatment system is designed such that the separation system is configured to be in fluid communication with the SCR catalyst through the first fuel outlet during operation. A system including the emission treatment system and a combustion engine is also provided. Method of increasing NOx reduction efficiency of the SCR catalyst using fuel fraction is discussed.

BACKGROUND

The invention relates generally to an efficient emission treatmentsystem and method of operating the emission treatment system.

Exhaust streams generated by the combustion of fossil fuels in, forexample, furnaces, ovens, and engines, contain nitrogen oxides (NOx)that are undesirable pollutants. There is a growing need to haveefficient and robust emission treatment systems to treat the NOxemissions.

In selective catalytic reduction (SCR) using hydrocarbons (HC),hydrocarbons serve as the reductants for NOx conversion. Hydrocarbonsemployed for HC-SCR include relatively small molecules like methane,ethane, ethylene, propane and propylene as well as longer linearhydrocarbons like hexane, octane, etc. or branched hydrocarbons likeiso-octane. The injection of several types of hydrocarbons has beenexplored in some heavy-duty diesel engines to supplement the HC in theexhaust stream. From an infrastructure point of view, it would beadvantageous to employ an on-board diesel fuel as the hydrocarbon sourcefor HC-SCR.

Fuels, including gasoline or diesel fuels containing sulfur lead to anumber of disadvantages when trying to clean-up the exhaust gases bysome form of catalytic after-treatment. During the combustion process,sulfur in the fuel gets converted to sulfur dioxide (SO₂), which poisonssome catalysts. Further poisoning happens from the formation of basemetal sulphates from the components of a catalyst compositions, whichsulphates can act as a reservoir for poisoning sulfur species within thecatalyst.

When the SCR catalysts absorb the NOx in the exhaust gas, they alsoabsorb sulfur oxides (SOx) in the exhaust gas. The sulfur oxides poisonthe catalysts, and the NOx absorption performance declines as thepoisoning by SOx increases.

In conventional NOx trap devices, the amount of SOx trapped at thecatalyst is computed and when the computed amount reaches an upperlimit, the air-fuel ratio of the air-fuel mixture supplied to engine istemporarily enriched and the exhaust gas temperature is increased. Dueto the increase of temperature of the exhaust gas, the SOx trapped bythe catalyst is released, and the NOx trapping performance of thecatalyst is recovered. This operation is termed desulfating of thecatalyst. Also in the NOx trapping systems, two sets of catalyst arerequired, so that one can be used while the other one is gettingregenerated. Therefore, it is desirable to have an emission treatmentsystem with properties and characteristics that has enhanced sulfurtolerance without severe degradation of the NOx reduction activity.

BRIEF DESCRIPTION

In one embodiment, an emission treatment system is presented. Theemission treatment system comprises a separation system and a selectivecatalytic reduction (SCR) catalyst. The separation system comprises aseparator, a fuel inlet disposed to supply fuel to the separator, afirst fuel outlet and a second fuel outlet respectively disposed tocarry away fuel from the separator. The SCR catalyst comprises acatalyst composition comprising silver and templated metal oxidesubstrate. The emission treatment system is designed such that theseparation system is configured to be in fluid communication with theSCR catalyst through the first fuel outlet during operation.

In one embodiment, a system is provided. The system includes a fuel tankadapted to supply a fuel, a combustion engine configured to receive thefuel and create an exhaust stream, and an emission treatment systemconfigured to receive at least a portion of the exhaust stream. Theemission treatment system includes a separation system and an SCRcatalyst. The separation system comprises a fuel inlet disposed toreceive fuel from the fuel tank, a separator configured to receive fuelthrough the fuel inlet, a first fuel outlet and a second fuel outletdisposed to carry away fuel from the separator. The SCR catalystcomprises a catalyst composition comprising silver and templated metaloxide substrate. The emission treatment system is designed such that theseparation system is configured to be in fluid communication with theSCR catalyst through the first fuel outlet during operation.

In one embodiment, a system is provided. The system includes a fuel tankadapted to supply a fuel, a combustion engine configured to receive thefuel and create an exhaust stream, and an emission treatment systemconfigured to receive at least a portion of the exhaust stream. Theemission treatment system includes a separation system and an SCRcatalyst. The separation system comprises a fuel inlet disposed toreceive fuel from the fuel tank, a separator configured to receive fuelthrough the fuel inlet and to separate the fuel using a flash heater totwo fractions: A first fraction having a maximum boiling point at atemperature in a range from about 70° C. to about 360° C. and a secondfraction having a boiling point above said temperature range. Theseparation system further comprises a first fuel outlet, and a secondfuel outlet. The SCR catalyst of the emission treatment system includesa catalyst composition comprising silver and a templated metal oxidesubstrate. In this embodiment, the separation system is in fluidcommunication with the SCR catalyst through the first fuel outlet andthe separation system is in fluid communication with the combustionengine through the second fuel outlet.

In one embodiment, a system is provided. The system includes a fuel tankadapted to supply a fuel, a combustion engine configured to receive thefuel and create an exhaust stream, and an emission treatment systemconfigured to receive at least a portion of the exhaust stream. Theemission treatment system includes a separation system and an SCRcatalyst. The separation system comprises a fuel inlet disposed toreceive fuel from the fuel tank, a separator configured to receive fuelthrough the fuel inlet and to separate the fuel using a flash heaterinto two fractions: A first fraction having a minimum boiling point at atemperature in a range from about 70° C. to about 360° C., and a secondfraction having a boiling point below said temperature range. Theseparation system further comprises a first fuel outlet, and a secondfuel outlet. The SCR catalyst of the emission treatment system includesa catalyst composition comprising silver and a templated metal oxidesubstrate. In this embodiment, the separation system is in fluidcommunication with the SCR catalyst through the first fuel outlet andthe separation system is in fluid communication with the combustionengine through the second fuel outlet.

In one embodiment, a method of reducing nitrogen oxides in an exhauststream is disclosed. The method comprises the steps of passing a fuelthrough a fuel inlet of a separation system, fractionating the fuel intoa first fraction and a second fraction using a separator in theseparation system such that the first fraction has a different averageboiling point than the second fraction, passing the first fractionthrough a first fuel outlet of the separation system to an SCR catalystand passing a second fraction through a second fuel outlet of theseparation system to a combustion engine. The SCR catalyst comprises acatalyst composition that includes silver and a templated metal oxidesubstrate. The combustion engine is configured to create the exhauststream and the SCR catalyst reduces nitrogen oxides present in theexhaust stream created by the combustion engine.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a system in accordance with oneembodiment of the invention;

FIG. 2 is a schematic diagram of a separation system in accordance withone embodiment of the invention;

FIG. 3 is a graphical representation of result of fuel sensitivityperformance experiment in accordance with one embodiment of theinvention;

FIG. 4 is a graph of experimental results for the performance of a GaAgmonolith with ULSD and biodiesel, in accordance with one embodiment ofthe invention;

FIG. 5 is a graphical representation of NOx reduction efficiencydegradation in accordance with one embodiment of the invention;

FIG. 6 is a graphical representation of NOx reduction efficiencydegradation in accordance with one embodiment of the invention;

FIG. 7 is a graphical representation of NOx reduction performation inaccordance with one embodiment of the invention;

FIG. 8 is a graphical representation of NOx reduction performation inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION

The systems and methods described herein include embodiments that relateto a system comprising internal combustion engines and emissiontreatment systems employed to treat the exhaust gases from thecombustion engines. The emission treatment systems include embodimentsthat relate to a system using the catalyst composition for reducingnitrogen oxides and separation systems that facilitate robustperformance of catalyst compositions. Generally, disclosed is a NOxselective reduction catalyst (SCR) and emission treatment system forreducing NOx in exhaust gas discharged from a combustion device.Suitable combustion devices may include furnaces, ovens, or engines.

In the following specification and the claims that follow, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise.

As used herein, without further qualifiers, “mesoporous” refers to amaterial containing pores with diameters in a range of from about 2nanometers to about 50 nanometers. A catalyst is a substance that cancause a change in the rate of a chemical reaction without itself beingconsumed in the reaction. Templating refers to a controlled patterning;and, templated refers to determined control of an imposed pattern andmay include molecular self-assembly. A monolith may be a ceramic blockhaving a number of channels, and may be made by extrusion of clay,binders and additives that are pushed through a dye to create astructure. Approximating language, as used herein throughout thespecification and claims, may be applied to modify any quantitativerepresentation that could permissibly vary without resulting in a changein the basic function to which it is related. Accordingly, a valuemodified by a term such as “about” is not to be limited to the precisevalue specified. In some instances, the approximating language maycorrespond to the precision of an instrument for measuring the value.All temperatures given herein are for the atmospheric pressure. Oneskilled in the art would appreciate that the boiling points can varywith respect to the ambience pressure of the fuel.

In one embodiment, a system is provided. The system comprises a fueltank, a combustion engine, and an emission treatment system. A fuel tankis a storage place for fuel or a continuous supply of fuel. Fuel may beof different kinds that are used to run the combustion engines. In oneembodiment, fuel comprises a material selected from the group consistingof diesel fuel, ultra low sulfur diesel (ULSD), biodiesel fuel,Fischer-Tropsch fuel, gasoline, ethanol, kerosene, and any combinationthereof. In a further embodiment, the fuel comprises diesel fuel orbiodiesel fuel. In one embodiment, the fuel comprises a non-biodieselfuel selected from the group consisting of diesel fuel, ULSD,Fischer-Tropsch fuel, gasoline, kerosene, and ethanol. In oneembodiment, the fuel comprises a non-biodiesel fuel selected from thegroup consisting of diesel fuel, ULSD, Fischer-Tropsch fuel, kerosene,and gasoline. In a further embodiment, the fuel comprises ULSD.

In another embodiment, the fuel comprises a biodiesel fuel or acombination comprising a biodiesel fuel. In a further embodiment, thefuel comprises a mixture of biodiesel fuel and at least onenon-biodiesel fuel. In a certain embodiment, the fuel comprises amixture of ULSD and biodiesel. In one particular embodiment, the ULSDfuel does not contain any intentionally premixed alcohols. In oneembodiment, while referring to a particular fuel, the fuel may comprisethe native ingredients and kerosene in the fuel. For example, in a fuelconsisting essentially of ULSD, there is no intentional pre-mixing ofany alcohols along with ULSD fuel. However, some amount of kerosene maybe present as a part of the commercial ULSD. In another example, in afuel consisting essentially of biodiesel, there is no intentionalpre-mixing of any alcohols along with biodiesel. However, a small amountof diesel and kerosene may be present as a part of the commercial orindigenous biodiesel. Similarly in a fuel mixture consisting essentiallyof ULSD and biodiesel, there is no intentional pre-mixing of anyalcohols along with ULSD and biodiesel. However, a small amount ofkerosene may be present as a part of the commercial or indigenous ULSDand biodiesel.

A combustion engine is any engine that accepts fuel, performs an actionby burning fuel and emits an exhaust stream. In one embodiment, thecombustion engine is an internal combustion engine in which thecombustion of a fuel occurs with an oxidizer in a combustion chamberresulting in an expansion of the high temperature and pressure gasesthat can be applied to move a movable component of the engine. Examplesof combustion engines include gasoline engines, diesel engines, andturbines.

An emission treatment system works on an exhaust stream of thecombustion engine and reduces harmful emissions in the exhaust stream.In one embodiment, the emission treatment system is configured toreceive at least a portion of the exhaust stream. Further, the treatmentsystem comprises a separation system that includes a separator, a fuelinlet to the separator, and at least two fuel outlets. The separatorseparates the contents of fuel into two fractions and sends out thefractions through the two fuel outlets. In general, the two fractionsare such that one fraction is a fuel component used, for example, forthe operation of the combustion engine, or for some other purpose, andthe other fraction is a reductant component, generally comprisingreductant species (“reductants”) suitable for use in NOx reduction.Apart from receiving one fraction of fuel from the separator, the enginemay or may not additionally receive fuel from the fuel tank directlydepending on the fuel fraction production and the requirement of thefuel in the engine and the reductant in SCR catalyst. Similarly, in oneembodiment, the fuel coming from the separator to the engine can beredirected fully or partially to the fuel tank or another temporarystorage tank depending on the fuel fraction production and therequirement of the fuel in the combustion engine at that time. At leasta portion of the fuel is burned in the engine during operation of theengine and an emission of exhaust gases are produced thereby. Theexhaust gases, thus produced, are discharged to an SCR catalyst of anemission treatment system, where the emission is treated.

FIG. 1 is a schematic diagram of an example of a system 10 comprising afuel tank 12 adapted to supply a fuel, a combustion engine 14 configuredto receive the fuel and create an exhaust stream, and an emissiontreatment system 16 configured to receive at least a portion of theexhaust stream. The emission treatment system 16 comprises a separationsystem 20 and an SCR catalyst 30. The separation system 20 comprises afuel inlet 22 disposed to receive fuel from the fuel tank 12, aseparator 24 configured to receive fuel through the fuel inlet 22, afirst fuel outlet 26 and a second fuel outlet 28 disposed to carry awayfuel from the separator 24. The separation system 20 is in fluidcommunication with the SCR catalyst 30 through the first fuel outlet 26.

In one embodiment, two fractions of the fuel are separated in theseparator based on the vapor pressures of the fractions. In a furtherembodiment, the fractions are separated based on their boiling points.In general, the smaller chain molecules such as, for example, methane,ethylene, and propylene are lighter and have lower boiling pointscompared to bigger molecules. In some embodiments, separation of lighterand heavier hydrocarbons can be carried out through separation based ontheir boiling points. In one embodiment, the lighter and heavierhydrocarbons can also be separated by mechanical separation means suchas membranes.

The fractionations using vapor pressure or boiling points can be carriedout in several ways. In one embodiment, the fuel is distilled attemperature and/or pressure ranges suitable for separating the requiredfractions. In another embodiment, the fuel is flash heated, passedthrough a bubble chamber, or subjected to a heat exchanger forfractionation. In one embodiment, the fraction of fuel having the higherboiling point is in the vapor state. In a further embodiment, thefraction of fuel in the vapor state is used as a reductant to the SCRcatalyst. In another embodiment, the fraction of fuel in the vapor stateis condensed, optionally stored, and then used as a reductant to the SCRcatalyst. In one embodiment, the fraction of fuel having lower boilingpoint is in the liquid state.

In another embodiment, the fractions are separated by the molecularsizes of the fuel. In one embodiment, the reductant is a hydrocarbonhaving an average carbon chain length of about 2 carbon atoms to about24 carbon atoms. In a further embodiment, the carbon chain length is inthe range of about 10 carbon atoms to about 16 carbon atoms. In oneembodiment, the reductant is an oxygenated hydrocarbon, such as ethanol.Fractionations by molecular sizes can be carried out using molecularsieves and/or membranes.

In one embodiment, the SCR catalyst 30 comprises a catalyst composition.In a further embodiment, the catalyst composition includes silver andtemplated metal oxide. The silver acts as a catalyst metal and thetemplated metal oxide acts as a catalyst substrate.

Suitable catalyst substrate may include an inorganic material. Suitableinorganic materials may include, for example, oxides, carbides,nitrides, hydroxides, carbonitrides, oxynitrides, borides, orborocarbides. In one embodiment, the inorganic oxide may have hydroxidecoatings. In one embodiment, the inorganic oxide may be a metal oxide.The metal oxide may have a hydroxide coating. Other suitable metalinorganics may include one or more metal carbides, metal nitrides, metalhydroxides, metal carbonitrides, metal oxynitrides, metal borides, ormetal borocarbides. Metallic cations used in the foregoing inorganicmaterials can be transition metals, alkali metals, alkaline earthmetals, rare earth metals, or the like.

In one embodiment, the catalyst substrate includes oxide materials. Inone embodiment, the catalyst substrate includes alumina, zirconia,silica, zeolite, or any mixtures comprising these elements. The desiredproperties of the catalyst substrate include, for example, a relativelysmall particle size and high surface area. In one embodiment, the powderof the catalyst substrate has an average diameter that is less thanabout 100 micrometers. In one embodiment, the average diameter is lessthan about 50 micrometers. In a further embodiment, the average diameteris from about 1 micrometer to about 10 micrometers. The catalystsubstrate powders may have a surface area greater than about 100m²/gram. In one embodiment, the surface area of the catalyst substratepowder is greater than about 200 m²/gram. In one embodiment, the surfacearea is in a range of from about 200 m²/gram to about 500 m²/gram, and,in another embodiment, from about 300 m²/gram to about 600 m²/gram.

One way of forming templated substrates is by employing templatingagents. Templating agents facilitate the production of catalystsubstrates containing directionally aligned forms. The templating agentmay be a surfactant, a cyclodextrin, a crown ether, or mixtures thereof.An example of a useful templating agent is octylphenol ethoxylate,commercially available as TRITON X-114®.

The catalyst substrate may have periodically arranged templated pores ofdetermined dimensions. The dimensions can include pore diameter, degreeof curvature, uniformity of the inner surface, and the like. The mediandiameter of the pores, in some embodiments, is greater than about 2 nm.The median diameter of the pores, in one embodiment, is less than about100 nm. In some embodiments, the median diameter of the pores is in arange from about 2 nm to about 20 nm. In another embodiment, thediameter is from about 20 nm to about 60 nm and in yet anotherembodiment, the diameter is from about 60 nm to about 100 nm. The poresin some embodiments have a periodicity greater than about 50 Å. Thepores in some embodiments have a periodicity less than about 150 Å. Inone embodiment, the pores have a periodicity in the range of from about50 Å to about 100 Å. In another embodiment, the pores have a periodicityin the range from about 100 Å to about 150 Å.

In certain embodiments, the pore size has a narrow monomodaldistribution. In one embodiment, the pores have a pore size distributionpolydispersity index that is less than 1.5. As used herein, thepolydispersity index is a measure of the distribution of pore diameterin a given sample. In a further embodiment, the polydispersity index isless than 1.3, and in a particular embodiment, the polydispersity indexis less than 1.1. In one embodiment, the distribution of diameter sizesmay be bimodal, or multimodal.

The catalyst composition can include a catalytic metal along with thecatalyst substrates. Suitable catalyst metal may include one or more ofgallium, indium, rhodium, palladium, ruthenium, and iridium. Othersuitable catalyst metal includes transition metal elements. Suitablecatalyst metal also includes one or more of platinum, gold, and silver.In one embodiment, the catalyst metal comprises silver. In oneparticular embodiment, the catalyst metal is substantially 100% silver.

The catalyst metal may be present in an amount of at least about 0.5mole percent of the substrate. In one embodiment, the catalyst metal ispresent in an amount equal to or greater than 3 mole percent of thesubstrate. In one embodiment, the amount of catalyst metal present isabout 6 mole percent of the catalyst substrate. In one embodiment, thecatalytic metal may be present in an amount in a range of from about 1mole percent to about 9 mole percent of the substrate.

The SCR catalysts can have different dopants that enhance reductionactivity and stability of the catalysts. In one embodiment, the dopantsmay be selected from the group consisting of zirconium, iron, gallium,indium, tungsten, zinc, platinum, and rhodium. In one embodiment, thedopant comprises zirconium. In another embodiment, the dopant comprisesrhodium and in yet another embodiment, the dopant comprises both galliumand indium. In one embodiment, the dopant may be present in an amount ina range of from about 0.1 mole percent to about 20 mole percent, of thesubstrate material. In a further embodiment, the dopant may be presentin an amount in a range of from about 0.1 mole percent to about 5 molepercent, of the substrate material. In a particular embodiment, thedopant may be present in an amount in a range of from about 0.5 molepercent to about 3 mole percent, of the substrate material.

One useful NOx reduction catalyst is silver-templated alumina (Ag-TA)catalyst. In some embodiments, the inventors studied the reductionefficiency of NOx reduction catalysts by taking Ag-TA as an example.

In one embodiment, the fuel fractionated based on the boiling point isused in the emission treatment system such that the lower boiling pointfraction is taken out through the first fuel outlet 26 to the SCRcatalyst 30. Trial evaluations of such a system have found this fractionto be a better reductant than the fuel itself. That is, the emissiontreatment system was found to be more efficient in NOx reduction whenthe lower boiling fraction of the fuel was used as a reductant incomparison with using a non-fractionated, stock fuel itself as areductant. An efficiency increase of the emission treatment system whenusing a lower boiling point fraction of the fuel was also observed withan emission treatment system having a sulfur treated HC-SCR catalyst. Asulfur treated catalyst is defined herein as a catalyst that is exposedto an amount of sulfur that is capable of reducing the performanceefficiency of the catalyst by more than about 5%. Use of lower boilingpoint fuel fraction for NOx reduction significantly improves the NOxconversion performance of the HC-SCR after sulfur treatment whencompared to the non-fractionated fuel. This property is particularlyuseful in applications where the catalyst is likely to experience somesulfur exposure. The advantages include improved performance of thecatalyst and hence lower usage amounts of catalyst. The fuels that arebeneficial for use as a lower boiling point fraction for increasedreduction efficiency of the NOx reduction HC-SCR catalyst include dieselfuel, ULSD, Fischer-Tropsch fuel, gasoline, ethanol, kerosene, and anycombination thereof. Tests have indicated that the lower boiling pointfraction of diesel is a better reductant than the higher boiling pointfraction of diesel on the Ag-TA catalyst.

In another embodiment, the fuel fractionated based on the boiling pointis used in the emission treatment system such that the higher boilingpoint fraction is taken out through the first fuel outlet 26 to the SCRcatalyst 30. In some situations, the higher boiling point fuel was foundto be a better reductant than the fuel itself by improving the NOxconversion performance of the HC-SCR. One example of a fuel that isbeneficial to be used as a higher boiling point fraction for increasedreduction efficiency of the NOx reduction HC-SCR catalyst is abiodiesel/diesel fuel mixture such as B20. One skilled in the art wouldpredict that a higher boiling point fraction of a mixture comprisingbiodiesel may also increase the reduction efficiency of the emissiontreatment system comprising a sulfur treated HC-SCR catalyst.

In one embodiment, separator 24 of the emission treatment system 16 isconfigured to receive fuel through the fuel inlet 22 and to separate thefuel into two fractions. A first fraction has a maximum boiling point ata temperature of about 360° C. and the second fraction of fuel has aboiling point above that of the first fraction. The maximum boilingpoint of a fraction as used herein denotes the theoretical temperatureat which all the ingredients of the fraction will evaporate, whensubjected to heating at atmospheric pressure.

In one embodiment, the separator 24 is configured to fractionate theincoming fuel into two fractions with a first fraction having a maximumboiling point at a temperature that ranges from about 70° C. to about360° C. and the second fraction of fuel having a boiling point abovethat of the first fraction. Therefore, depending on the maximum boilingpoint of the first fraction, the second fraction of this fractionationmay have a minimum boiling point greater than a temperature that rangesfrom about 70° C. to about 360° C. In one embodiment, the separator 24is configured to fractionate the incoming fuel into two fractions with afirst fraction having a maximum boiling point at a temperature thatranges from about 100° C. to about 225° C. and the second fraction offuel having a boiling point above that of the first fraction. In afurther embodiment, the temperature of separation of two fractions isabout 225° C.

In another embodiment, the separator 24 is configured to fractionate theincoming fuel into two fractions with a first fraction having a minimumboiling point at a temperature that is in a range from about 70° C. toabout 360° C. and the second fraction of fuel having a boiling pointbelow that of the first fraction. Therefore, depending on the minimumboiling point of the first fraction, the second fraction of thisfractionation may have a maximum boiling point lower than a temperaturethat ranges from about 70° C. to about 360° C. In a further embodiment,the first fraction has a minimum boiling point at a temperature that isin a range from about 225° C. to about 360° C. and the second fractionof fuel that has a boiling point below that of the first fraction. In afurther embodiment, the minimum boiling point of the first fraction isat a temperature that is in the range of about 300° C. to about 360° C.

Depending on the type of fuel used and advantage of using low boilingpoint fraction or high boiling point fraction for the efficiencyincrease of the SCR catalyst, the suitable fuel fraction can betransferred to the SCR catalyst 30, and the other fraction can be routedto the combustion engine 14 or to a storage tank, as required. Forexample, in one embodiment, the separator function is fixed in providinga first fraction of low boiling point fuel and a second fraction of highboiling point fuel, and the separator outlets 26, 28 feeding the SCRcatalyst 30 and combustion engine 14 respectively, are switcheddepending on the fuel fractionation. In another embodiment, keeping thefirst fuel outlet 26 and second fuel outlet 28 fixed to the SCR system30 and the combustion engine 14 respectively, the function of theseparator is modified in providing a first fraction of lower boilingpoint or higher boiling point fuel, depending on the requirement. Thus,by adjusting the outlet connection or the separator function, eachfraction is routed to the proper outlet, depending on which fraction(high boiling point or low boiling point) is desired for use as areductant.

In one embodiment, a method of reducing nitrogen oxides in an exhauststream is disclosed. The method comprises the steps of passing a fuelthrough a fuel inlet 22 (FIG. 1) of a separation system 20 andfractionating the fuel into a first fraction and a second fraction usinga separator 24 in the separation system 20 such that the first fractionhas a different average boiling point than the second fraction. Theaverage boiling point as used herein denotes the mean boiling point ofthe total constituents of a particular fraction, averaged to accommodatedifferent variations such as, for example, the operators, source offuel, ambient temperatures, and type of separation equipment.

The method further includes passing the first fraction through a firstfuel outlet 26 of the separation system 20 to an SCR catalyst 30. TheSCR catalyst 30 used herein comprises a catalyst composition thatincludes a silver catalyst and a templated metal oxide substrate. Thesecond fraction of fuel can be directly fed to the combustion engine 14,fed back to the fuel tank 12 or partially or fully stored in a storagetank (not shown). In one embodiment of the method, the second fractionof the fuel passes through a second fuel outlet 28 of the separationsystem 20 to a combustion engine 14. In one embodiment, the secondfraction of fuel is not fed back into the fuel tank that supplies fuelto the separation system 20. In one embodiment, the combustion engineoperates on the second fraction of fuel received from the separationsystem 20 and creates an exhaust stream that is fed into the SCRcatalyst 30 to reduce the harmful emissions of the exhaust stream. Inone particular embodiment, the SCR catalyst 30 is used to reduce thenitrogen oxides present in the exhaust. In one embodiment, thecombustion engine receives fuel from a fuel tank or fuel line inaddition to the second fraction of fuel from the separation system 20.

In one embodiment of the method, the first fraction of fuel has a loweraverage boiling point than the second fraction of fuel. The temperatureof separation of two fractions in this embodiment is in the range ofabout 70° C. to 360° C. In one embodiment, the first fraction has amaximum boiling point that is less than about 360° C. The fuels that arenormally used in this embodiment include diesel fuel, ULSD,Fischer-Tropsch fuel, gasoline, ethanol, kerosene, or any combinationsthereof. In a further embodiment, the first fraction has a maximumboiling point in the temperature range of about 100° C. to 225° C. In anassociated embodiment, the first fraction has a maximum boiling point inthe temperature range of about 150° C. to 200° C. The fuel that isnormally used in this embodiment includes a diesel fuel and/or ULSD. Ina further embodiment, the fuel consists essentially of ULSD. In anassociated embodiment, an ULSD fuel is fractionated at a temperature ofabout 200° C. and the less boiling point fraction is used as reductantfor NOx reduction. In a further embodiment, the portion not used as areductant is used as engine fuel.

In an alternate embodiment of the method, the first fraction of fuel hasa higher average boiling point than the second fraction of fuel. Thetemperature of separation of two fractions in this embodiment is in therange of about 70° C. to 360° C. Therefore, the first fraction has aminimum boiling point that is equal to or greater than about 70° C. Thefuels that are normally used in this embodiment include biodiesel fuel,diesel, ULSD, Fischer-Tropsch fuel, kerosene, or any combinationsthereof. In a particular embodiment of the method, the temperature ofseparation of two fractions is in the range of about 250° C. to 360° C.Therefore, the first fraction has a minimum boiling point that is equalto or greater than about 250° C. One fuel that is normally used in thisembodiment includes a mixture of biodiesel fuel and ULSD. In thisembodiment, when the separator separates the fuel into two fractions,the first fraction is expected to consist essentially of biodiesel fuelthat is fed into the SCR catalyst 30. The second fraction is expected toconsist essentially of ULSD that is fed into the combustion engine 14,recirculated to the fuel tank 12, or stored in a storage tank forfurther usage. In a further embodiment, the temperature of separation oftwo fractions is in the range of about 300° C. to 360° C. In anassociated embodiment, the first fraction has a minimum boiling point inthe range of about 300° C. to 360° C. An example of a fuel that may besuitably applied in this embodiment includes biodiesel fuel.

In one embodiment, multiple separators 24 can be used to fractionate thefuel and advantageously feed the desired fractions to the SCR catalyst30 and the combustion engine 14 or to the fuel storage tank. Forexample, in one embodiment, a fuel can be fractionated in threedifferent temperature zones using two separators as shown in FIG. 2. InFIG. 2, the separation system 20 comprises a first separator 24 and asecond separator 34, such that the first fuel outlet 26 of the firstseparator is the fuel inlet 26 of the second separator 34. The fuelfractionated by the second separator 34 has a first fuel outlet 36 and asecond fuel outlet 38. Depending on the requirement of the reductant forhigher efficiency, any one fraction of the fuel, or any combinations oftwo fractions of fuel can be fed in to the SCR system 30. In oneexample, fuels having maximum boiling points above, for example, 100° C.may be separated using a separator and another separator can be used tofurther separate the fuel having maximum boiling point above, forexample, 225° C. Thus in the above example, the fuels can befractionated into three fractions: a first fraction with a maximumboiling point of 100° C., a second fraction with a minimum boiling pointof 100° C. and maximum boiling point of 225° C. and a third fractionwith a minimum boiling point of 225° C. If the initial stock fuelconsisted essentially of ethanol, ULSD, and biodiesel, then, in oneembodiment, the SCR catalyst performance can be increased by passing thefirst and third fractions as reductants while using the second fractionfor the functioning of combustion engine. In one embodiment, a singleseparator 24 can be operated at different temperatures at differenttimes, depending on the variations such as, for example, type of theinlet fuel and type of SCR catalyst used.

The SCR catalyst 30 advantageously functions across a variety oftemperature ranges. In one embodiment, the catalyst composition reducesthe nitrogen oxides at a temperature greater than about 275° C. In afurther embodiment, the catalyst composition reduces NOx at atemperature greater than about 325° C.

EXAMPLES

The following experiments were carried out for determining thesensitivity of NO_(x) catalyst to reductant composition by usingdifferent fractions of diesel fuels taken from different sources.

An Ag-TA catalyst composition in the form of a washcoated monolith wasconsidered as the catalytic material. In order to understand the effectof reductant on a fresh catalyst, the monolith used herein was usedwithout being subjected to sulfur treatment. The feed gas compositionincluded 300 ppm NO, 7% H₂O, and 9% O₂. Two different base ULSD fuelswere compared: One is a ULSD fuel blend designed for winter andidentified as ULSD-1, and another is a ULSD fuel blend designed forsummer and identified as ULSD-2. These compositions are the variationsof the stock fuel that are generally used as a reductant in studiesperformed in a reactor that mimics an exhaust treatment system of alocomotive engine. Fractions were distilled from these two ULSD stockfuels. The fractionation was performed from room temperature up to a cutoff temperature of 200° C. and the portion that was vaporized andcondensed was retained and named as fraction 1. Temperature of reductionfor these experiments were considered as 450° C., 400° C., 350° C., and300° C. with 1 hour of hold at each temperature.

Some of these fuels were tested using gas chromatography (GC) andNuclear Magnetic Resonance Spectroscopy (NMR). From the results of theseanalytical tests (Not shown), it was observed that the ULSD-1 had a muchlighter composition than ULSD-2. One reason for the difference incomposition between the ULSD-1 and ULSD-2 may be a possible addition ofkerosene in the commercial winter blend (ULSD-1) to lighten the fuel forwinter in colder climates. The fractionation process cuts out the longerchain, higher boiling constituents in the ULSD.

The ULSD-1 and ULSD-2 fuels and fractions 1 of the ULSD-1 and ULSD-2fuels were used as reductants to determine the sensitivity of a Ag-TAcatalyst to reductant composition. The results of these fuel sensitivityperformance experiments are shown in FIG. 3. It is clear that thecatalyst was sensitive to the reductant composition, with the highestNO_(x) conversion 52 and 54 coming from the fraction 1 of the ULSD-1 andULSD-2, respectively, compared to the unfractionated ULSD-1 and ULSD-2.Between the unfractionated ULSD stock fuels, ULSD-1 resulted in higherNOx conversion 56 than the NOx conversion 58 of ULSD-2, which is likelydue to the higher concentration of heavy molecules and/or aromaticmolecules in the ULSD-2 stock fuel.

FIG. 4 compares a NOx reduction performance of diesel, biodiesel and amixture of diesel and biodiesel (called as B20) while using a washcoatedmonolith using GaAg catalyst for NOx reduction. The comparison showsthat biodiesel was a more effective reductant than the diesel or themixture of diesel and biodiesel.

The NOx reduction efficiency degradation due to sulfur poisoning wasstudied in the labs. The degradation of the Ag-TA catalyst performanceduring the use of ULSD fuel was studied for a fresh catalyst and acatalyst that had a deep sulfur (S) treatment with 30 ppm SO₂ for 12 hrsat 350° C., and then tested over a wide temperature range. Steady stateperformance at temperatures lower than 400° C. was strongly affected bythe deep S treatment, as can be observed from the comparison of NOxreduction activity curve of the fresh catalyst 62 and the sulfur treatedcatalyst 64 (FIG. 5).

NOx profile as a function of time revealed an interesting feature for asulfur (S) treated monolith washcoated with Ag-TA catalyst and tested at375° C. (FIG. 6). NOx conversion reached ˜50% soon after ULSD addition,and then rapidly decreased to the steady state value of about 10% in thenext 5 minutes. One possible explanation is that carbon is accumulatingon the surface upon diesel addition, and affects the performance. Itappears that the process is accelerated upon S exposure. This indicatesthat deep S treatment deteriorates the ability of the catalyst to removeaccumulations of carbonaceous by-products (coke). Therefore, onepotentially attractive strategy is to use fractionated diesel asreductant, as the heavier fractions in diesel are likely be the primarysource for carbon formation.

To test this hypothesis, the performance of the S treated Ag-TA catalystmonolith was evaluated with lighter fraction of diesel (boilingpoint<200° C.). The NOx reduction performance of the catalyst was higherfor a fractionated diesel 66 than the unfractionated diesel fuel 68 inthe temperature range of about 325° C. to about 375° C. as shown in FIG.7. Moreover, the NOx activity as a function of time profile indicatedthat the catalyst deactivation due to coking was higher for the ULSD 72in comparison with the fractionated diesel 74 as shown in FIG. 8. Thissuggests that the emission treatment system comprising Ag-TA catalystcomposition had a higher sulfur tolerance when the fractionated fuel wasused in comparison with unfractionated fuel.

The system and methods discussed herein can be applied for improving theoverall NO_(x) conversion of the after treatment system. The presentstudy suggests different diesel formulations may have varying effects onthe catalyst. The system and methods described herein may limit thevariability of NOx conversion as a function of fuel source as it wouldalways take a beneficial fraction from the fuel and eliminate theunfavorable fraction that is likely to be the cause of coking of thecatalyst.

The embodiments described herein are examples of composition, system,and methods having elements corresponding to the elements of theinvention recited in the claims. This written description may enablethose of ordinary skill in the art to make and use embodiments havingalternative elements that likewise correspond to the elements of theinvention recited in the claims. The scope of the invention thusincludes composition, system and methods that do not differ from theliteral language of the claims, and further includes other compositionsand articles with insubstantial differences from the literal language ofthe claims. While only certain features and embodiments have beenillustrated and described herein, many modifications and changes mayoccur to one of ordinary skill in the relevant art. The appended claimscover all such modifications and changes.

1. An emission treatment system comprising: a separation systemcomprising a separator, a fuel inlet disposed to supply fuel to theseparator, a first fuel outlet and a second fuel outlet respectivelydisposed to carry away fuel from the separator; and a selectivecatalytic reduction (SCR) catalyst comprising a catalyst compositioncomprising silver and templated metal oxide substrate, wherein theseparation system is configured to be in fluid communication with theSCR catalyst through the first fuel outlet during operation.
 2. Theemission treatment system of claim 1, wherein the separator comprises aflash heater.
 3. The emission treatment system of claim 1, wherein theseparator comprises a distillation unit.
 4. The emission treatmentsystem of claim 1, wherein the separator comprises a membrane.
 5. Theemission treatment system of claim 1, wherein the separator comprises aheat exchanger.
 6. The emission treatment system of claim 1, wherein theseparator comprises a bubbling column.
 7. The emission treatment systemof claim 1, wherein the templated metal oxide comprises alumina orsilica-alumina.
 8. The emission treatment system of claim 1, wherein thecatalyst composition has a surface area in the range of about 250 toabout 600 m²/gm.
 9. The emission treatment system of claim 1, whereinthe templated metal oxide has periodically arranged templated pores,wherein the average diameter of the pores is in a range of from about 2nanometers to about 100 nanometers and the pores have a periodicity in arange of from about 50 Angstrom to about 130 Angstrom.
 10. The emissiontreatment system of claim 1, wherein the substrate further comprises anadditional dopant material selected from the group consisting ofzirconium, yttrium, iron, gallium, indium, tungsten, zinc, platinum, andrhodium.
 11. The emission treatment system of claim 1, wherein theseparator is configured to receive fuel through the fuel inlet, separatethe fuel into a first fraction having a maximum boiling point at atemperature that is in the range from about 70 degrees Celsius to about360 degrees Celsius and a second fraction of fuel having a boiling pointabove said temperature, and dispose the first fraction into the firstfuel outlet.
 12. The emission treatment system of claim 11, wherein themaximum boiling point is at a temperature that is in the range fromabout 100 degrees Celsius to about 225 degrees Celsius.
 13. The emissiontreatment system of claim 12, wherein the temperature is about 225degrees Celsius.
 14. The emission treatment system of claim 1, whereinthe separator is configured to receive fuel through the fuel inlet,separate the fuel into a first fraction having a minimum boiling pointat a temperature that is in the range from about 70 degrees Celsius toabout 360 degrees Celsius and a second fraction of fuel having a boilingpoint below said temperature, and dispose the first fraction into thefirst fuel outlet.
 15. The emission treatment system of claim 14,wherein the minimum boiling point is at a temperature that is in therange from about 300 degrees Celsius to about 360 degrees Celsius. 16.The emission treatment system of claim 1, wherein the separation systemcomprises a first separator and a second separator, and wherein thefirst fuel outlet of the first separator is the fuel inlet of the secondseparator.
 17. A system comprising: a fuel tank adapted to supply afuel; a combustion engine configured to receive the fuel and create anexhaust stream; and an emission treatment system configured to receiveat least a portion of the exhaust stream wherein the emission treatmentsystem comprises: a separation system comprising a fuel inlet disposedto receive fuel from the fuel tank, a separator configured to receivefuel through the fuel inlet, a first fuel outlet and a second fueloutlet respectively disposed to carry away fuel from the separator; andan SCR catalyst comprising a catalyst composition comprising silver anda templated metal oxide substrate, wherein the separation system is influid communication with the SCR catalyst through the first fuel outlet.18. The system of claim 17, wherein the separation system is in fluidcommunication with the combustion engine through the second fuel outlet.19. The system of claim 17, wherein the separator comprises a flashheater.
 20. The system of claim 17, wherein the separator comprises adistillation unit.
 21. The system of claim 17, wherein the templatedmetal oxide comprises alumina or silica-alumina.
 22. The system of claim17, wherein the catalyst composition has a surface area in the range ofabout 250 to about 600 m²/gm.
 23. The system of claim 17, wherein thetemplated metal oxide has periodically arranged templated pores, whereinthe average diameter of the pores is in a range of from about 2nanometers to about 100 nanometers and the pores have a periodicity in arange of from about 50 Angstrom to about 130 Angstrom.
 24. The system ofclaim 17, wherein the substrate further comprises an additional dopantmaterial selected from the group consisting of zirconium, yttrium, iron,gallium, indium, tungsten, zinc, platinum, and rhodium.
 25. The systemof claim 17, wherein the separator is configured to receive fuel throughthe fuel inlet, separate the fuel into a first fraction having a maximumboiling point at a temperature that is in the range from about 70degrees Celsius to about 350 degrees Celsius and a second fractionhaving a boiling point above said temperature, and dispose the firstfraction into the first fuel outlet.
 26. The system of claim 25, whereinthe maximum boiling point is at a temperature that is in the range fromabout 100 degrees Celsius to about 225 degrees Celsius.
 27. The systemof claim 26, wherein the maximum boiling point is at a temperature thatis in the range from about 150 degrees Celsius to about 200 degreesCelsius.
 28. The system of claim 17, wherein the separator is configuredto receive fuel through the fuel inlet, separate the fuel into a firstfraction having a minimum boiling point at a temperature that is in therange from about 70 degrees Celsius to about 350 degrees Celsius and asecond fraction having a boiling point below said temperature, anddispose the first fraction into the first fuel outlet.
 29. The system ofclaim 28, wherein the minimum boiling point is at a temperature that isin the range from about 300 degrees Celsius to about 360 degreesCelsius.
 30. A system comprising: a fuel tank adapted to supply a fuel;a combustion engine configured to receive the fuel and create an exhauststream; and an emission treatment system configured to receive at leasta portion of the exhaust stream wherein the emission treatment systemcomprises: a separation system comprising: a fuel inlet disposed toreceive fuel from the fuel tank, a separator configured to receive fuelthrough the fuel inlet, separate the fuel using a flash heater to afirst fraction having a maximum boiling point at a temperature that isin the range from about 70 degrees Celsius to about 360 degrees Celsiusand a second fraction having a boiling point above said temperaturerange, dispose the first fraction from the separator to a first fueloutlet, and dispose the second fraction from the separator to a secondfuel outlet; and an SCR catalyst comprising a catalyst compositioncomprising silver and a templated metal oxide substrate, wherein theseparation system is in fluid communication with the SCR catalyst andcombustion engine through the first fuel outlet and second fuel outlet,respectively.
 31. A system comprising: a fuel tank adapted to supply afuel; a combustion engine configured to receive the fuel and create anexhaust stream; and an emission treatment system configured to receiveat least a portion of the exhaust stream wherein the emission treatmentsystem comprises: a separation system comprising: a fuel inlet disposedto receive fuel from the fuel tank, a separator configured to receivefuel through the fuel inlet, separate the fuel using a flash heater to afirst fraction having a minimum boiling point at a temperature that isin the range from about 70 degrees Celsius to about 360 degrees Celsiusand a second fraction having a boiling point below said temperaturerange, dispose the first fraction from the separator to a first fueloutlet, and dispose the second fraction from the separator to a secondfuel outlet; and an SCR catalyst comprising a catalyst compositioncomprising silver and a templated metal oxide substrate, wherein theseparation system is in fluid communication with the SCR catalyst andcombustion engine through the first fuel outlet and second fuel outlet,respectively.
 32. A method of reducing nitrogen oxides in an exhauststream, comprising: passing a fuel through a fuel inlet of a separationsystem; fractionating the fuel into a first fraction and a secondfraction using a separator in the separation system, wherein the firstfraction has a different average boiling point than the second fraction;passing the first fraction through a first fuel outlet of the separationsystem to an SCR catalyst comprising a catalyst composition comprisingsilver and a templated metal oxide substrate; and passing a secondfraction through a second fuel outlet of the separation system to acombustion engine, wherein the combustion engine is configured to createthe exhaust stream and the SCR catalyst reduces nitrogen oxides presentin the exhaust stream created by the combustion engine.
 33. The methodof claim 32, wherein the catalyst composition reduces the nitrogenoxides at a temperature greater than about 275 degrees Celsius.
 34. Themethod of claim 32, wherein the fuel comprises at least one elementselected from the group consisting of diesel fuel, ULSD, biodiesel fuel,Fischer-Tropsch fuel, gasoline, kerosene, and ethanol.
 35. The method ofclaim 32, wherein the fuel comprises at least one of ultra low sulfurdiesel fuel and biodiesel.
 36. The method of claim 32, wherein the fuelcomprises ultra low sulfur diesel fuel.
 37. The method of claim 32,wherein the first fraction in first fuel outlet comprises lower boilingpoint fuel than the second fraction.
 38. The method of claim 37, whereinthe first fraction comprises at least one compound selected from thegroup consisting of an alcohol, kerosene, and ester.
 39. The method ofclaim 37, wherein the first fraction comprises the fuel in a vaporstate.
 40. The method of claim 37, wherein the first fraction has amaximum boiling point less than about 360 degrees Celsius.
 41. Themethod of claim 40, wherein the maximum boiling point is in the rangefrom about 100 degrees Celsius to about 225 degrees Celsius.
 42. Themethod of claim 32, wherein the first fraction in first fuel outletcomprises higher boiling point fuel than the second fraction.
 43. Themethod of claim 42, wherein the first fraction comprises biodiesel. 44.The method of claim 42, wherein the first fraction comprises the fuel ina liquid state.
 45. The method of claim 42, wherein the first fractionhas a minimum boiling point greater than about 250 degrees Celsius. 46.The method of claim 45, wherein the minimum boiling point is in thetemperature range from about 300 degrees Celsius to about 360 degreesCelsius.